Frequency selective surface (FSS) filters are commonly used with antenna systems for providing multiple frequency rejection bands. Some of these filters use dielectric substrates or other materials that are substantially transparent to electromagnetic signal transmissions. Some of the surfaces suggest elements that provide a number of frequency rejection bands. Other similar devices are formed as spatial filters that are positioned separate from an antenna or phased array antenna system. The filters are situated in the aperture plane for reducing the amplitudes of spatial sinusoidal field distribution in the main beam region of a radiation pattern associated with the antenna system. Some of the devices also include radiation absorbing material placed within the aperture plane or various elements within the aperture plane for modifying amplitude or filtering frequencies.
In commonly assigned U.S. Pat. Nos. 6,052,098 and 6,195,062, parasitic antenna elements are provided adjacent to an array of dipole elements of an antenna and formed as patterned conductor elements on one surface of a thin dielectric substrate. Feed elements for the driven dipole array comprise patterned conductor elements formed on an opposite surface of the substrate. The feed elements have a geometry with a mutually overlapping projection relationship with the conductors of the driven dipole elements to form a matched impedance transmission line to the dielectric substrate with the pattern dipole elements. Further addition of dipoles to that structure could provide a spatial filter surface for enhancing the reduction of sidelobes.
It would be more advantageous, however, if a spatial filtering surface can provide for magnitude and phase tapers and be applied to many different types of reflector antenna and phased antenna arrays made of elements with uniform weights where electronics required for the weights and amplitude and phase do not have to be implemented at the array level.